Method of forming gears



y 1930- E. WILDHABER 1,759,333

METHOD OF FORMING GEARS I Filed July 20, 1927' 3 Sheets-Sheet 1 May 20, 1930. I I E. WILDHABER 9,

METHOD 0? FORMING GEARS Filed July'zo, 1927 3 Sheets-Sheet 2 Fl G21 m g 12s 13s 13+ I H m f wrap: J I

no 138 m 151 mm 1 May 20, 1930. E. WILDHABER 1,759,333

' METHOD OF FORMING GEARS Filed July 20, 1927 3 Sheets-Sheet 5 INVENTOR EA/ b mum-1k Patented May 20, 1930 PATENT OFFICE ERNEST WILDHABEB, OF FROOKLYH, NEW YORK METHOD- ,or ronmme GEARS Application filed .Iuly 20, 1927. Serial No. 207,280. v

The present invention relates to methods of forming gears, and particularl to such methods in which a forming 'mem er and a gear blank are rotated in timed relation to each other, to form teeth on said gear.

The invention is applicable to forming gears by cutting as well as to forming gears by grinding, by lapping, by burnishing, and may be applied generally toforming gears by removing stock, whether small amounts of stock or large amounts are to be removed.

One object of the present invention is to I provide a novel method of finishing the tooth sidesof gears with speed and accuracy. A

further object is to devise a method of forming gears in a continuous process with a forming member ofnovel configuration. A further. aim is to devise a practical grinding method for forming gears in a continuous operation, with a grinding member having grinding portions disposed in a thread.

Methods for grinding gears in a continuous process with grinding members having grinding portions disposed in a thread hitherto required an excessive amount of time for truing or dressing said members to the required shape.

It is a further aim of the present invention to provide an' accurate and quick truing or dressing operation. for grinding members having grinding portions disposed in athread or threads.

Grinding members hitherto'provided for forming gears'in a continuous operation and with continuous grinding contact, had grinding portions disposed in a helical thread of straight profile in'axial section. The grinding member then represents the surface of a 4o helical screw. In one case, a grinding member' of this known type meshes with the finished teeth of a blank theoretically with point contact only, and therefore acts only on small portions at a time. In another case, a helical grinding member contains a straight profile (in axial section), disposed at right angles or substantially at right angles to its axis. While such a grinding member may contact alon lines with the teeth of a blank, it does I not orm theoretically correct tooth profiles.

.It is a further aim of the present invention to provide a m'ethod making use of a grinding member having grinding portions arranged in a thread, which is conjugate to a gear blank so as to mesh with line contact with said blank, while producing theoretically accurate gears.

A further aim is to provide a method of grinding gears with a member havin grind- .ing portions arranged in a thread 0t curved axis, so as to furnish a maximum of grinding contact.

A still other object is to devise a method of grinding gears in a continuous operation with a member having grinding portions disposed in a thread, which is suited to contact with a gear blank along a line extending substantially along a tooth profile, that is to say along a line reaching from the root directly to the point or tip of the teeth.

A further purpose is to provide a continuation of my invention as disclosed in my application entitled Method of cutting gear teeth filed March 2, 1925, Serial No. 12,572.

Numerous other objects will 'be apparent in the course of thespecification and from recital of the appended claims.

'My invention will be described with reference to examples illustrated in the accompanyin drawings, in which Fig. 1 is a plan view 0 a gear blank and dressing member, and of a grinding memberin engagement with said gear blank.

Fig. 2 is a front elevational View corresponding to Fig. 1.

Fig. 3 is a view, partly in section, of a pair of grinding members in enga ement with op-. posite tooth sides of a gear b ank.

Fig 4: is a plan view of a helical gear blank with said gear.

and of a grlnding member in engagement I Fig. 5 is a front elevational view corre-.

sponding to Fig. 4. I

Fig. 6 is a diagrammatic end view of a member, such as may be used in accordance with my invention.

7 member, corresponding to straight teeth.

Fig. 11 is a front elevational view of a truing member of the type illustrated in i 12 is a develo ment of a pair of truin'g mem rs correspon ing to helical teeth.

Fig. 13 and Fig. 14 are a diagrammatic 'go front view and corresponding side view of a grinding member and a truing member of further modified structure, the two mem-. bers being shown in' engagement with each.-

other.

Fig. 15 is a dia ammatic plan view of a machine for grin ing gears in accordance with my method.

Fig. 16 is a partial front elevation of the same.

Fig. 17 is a side view and section of the blank slide, also showing a grindin member in engagement with a blank, an corresponding to Figures 15 and 16.

' .Fig. 18 is a diagram illustrative of the different positions of a driving pinion relative- -l to its mating gear, in different phases of t e life of a grinding member, in the embodimentofmy invention as illustrated in the Fi res 15-17.

. ig. 19 is a schematic section of a gear box, which ma be'disposed adjacent a grindmg motor, an which furnishes a'slow speed for truin or (1 m4 5 in addition to a standard grinding speed Fig. 20 1s a plan view, partly a section of an auxiliary device such as may be provided in a machine as illustrated in the Figures 15-17.

Fig. 21 and Fig. 22 are diagrams illustrative of the driving arrangement for truin re erence to the Figures 13 and 14.

Fifi 23 is a diagram illustrative of means for e ective reciprocating feed in a machine for grinding gears. A

In the Figures 1 and 2 the numeral 11 denotes a gear blank secured to anarbor or shaft 12. Arbor 12 is journalled in bearings,

of which one is shown at 13, and carries a truing or dressing member 14 rigidl secured to said arbor. A grinding mem r 15 is rotatable on an axis'16, and 1s provided with ding portions disposed inathread or t eads 17. The blank 11 isfprovided with straight teeth 18 which extend along. its axis.

' the in a manner as will be described with.

The

in known methods of the character re ferred to, thethread of the grinding or cutting member has the,form of a screw thread, with straight profile inaxial section, and is ordinarily con ugate or approximately conjugate to the basic rack,to which the gear blank is also conjugate. I

According to the present invention the thread 17 of the grindiiig membe'r is directly conjugate to the teeth 18 of blank 11, so that it meshes with line contact with said blank, simultaneous contact being made along a line, which during the mesh moves on the tooth surface of the blank. The whole extent or a part of the tooth surfaces may be swept during every revolution. of the blank,

depending on whether the face 'of the gear blank is narrow or wide. Contact between grinding thread and the teeth of a blank is e ected ordinarily along the profilesof the blank, or rather along lines which 'are inclined only-by small angles to said profiles. g

The thread of the grinding member contains therefore profileswhich are nearly equal to the profiles of the teeth 'of the blank. It is noted that the profiles of the grinding threads are curved, and that they change their inclination to the axis 16 of a thread.

My method of grinding has a certain resemblance to 'grindin with a formed disk wheel having a pro e equal to the profile of a blank, inasmuch as grinding contact is effected in a'somewhat similar manner. My method differs from the said method b effecting continuous grinding contact wit a rotating blank, andtherefore by finishing all the teeth simultaneously, whereas in the known method referred to the different tooth spaces are. successively finished, and the blank is periodically indexed. I

In operation, the grinding member is turned on its axis 16 and the blank is turned on its axis 12 in timed relation. When the grinding member is provided with a single thread, that is to say when the adjacent fportions 20, 21 belong to successive turns 0 the. same thread, the grinding member is rotated a number of revolutions equal to the number of teeth in' the blank per revolution of the blank. In general the number of revolutions of grinding member and blank are inversely proportional to the respective numbers. of teeth or threads. Although grinding members may be devised, WhlCh cover the entire tooth surfaces while rotating in a single relative position, nevertheless a feeding motion is preferably provided, when the gear blank contains straight or helical teeth of constant ceding motion is found to furnis gears of greatun formity in lengthwise direction, irrespective of wear of the grindinmember. The feeding motion may consist o a motion the teeth of the blank, and is then lead of said motion being equal to the lead of said teeth. The feed motion is then comosed of a translation in the direction of the lank axis and an additional rotation on said axis.

The said feeding motion may be embodied as a single motion per grinding operation, or as a repeated or periodical motion of reciprocating nature. Embodiment as a single motion can be effected with a very simple structure, as will be explained with reference to the Figures 15-17. Means for obtaining a suitable eriodical feeding motion are described with reference to Fig. 23.

When grinding straight tooth gears (Fig. 1 and Fig. 2) ,the axis of a grinding member is vzpreferably set at right angles to the axis of the blank, provided that a grinding member of single thread is used, as shown in the drawings. I may however also set the grinding member to its average lead angle, or to any other suitable angle within a range which comprises the different angles at which the direction of the thread of the grinding member fits the direction of the teeth of the blank sufliciently to avoid an excessive fillet at the root of the teeth of the blank. It is found that by setting the grinding member to its said lead angle the thickness of its thread is a 7 maximum, and that a different inclination angle reduces slightly the thickness of the grinding thread to be used. The position of the grinding member also affects the fillet of the teeth, which connects the tooth profile proper with the bottom of a tooth space. The fillet is not suited to transmit motion and is therefore kept small, an aim which is ordinarily obtained without effort, unless the grinding member is set tb an angle diifering excessively from the said lead angle.

Setting .the' grinding member at right angles to the axis of the blank is found to produce satisfactory results for grinding straight tooth gears, and is ordinarily preferred on account of the structural simplicity.

When grinding gears without feed motion, however, the grinding member is preferably set to its lead angle, in which case the whole length of face of the teeth can be more easily covered on both tooth sides. together, because it is found that tooth contact of both tooth sides then has a more nearly equal position lengthwise of the face of-the gear. a

In any case the thread surface of the grindmg definite character. It is the surfacewhich at a given'relative positionof'the' respective centers is conjugate to the finished tooth sides of a van gear blank, in such manner asto mesh with line contactwith said tooth sides. In

other words it is a surface, such as is swept member is a surface of mathematically out or enveloped by a tooth surface of the blank in its relative path with respect to said member.

One way of obtaining such a surfaceis by providing a cutting edge extending on the tooth surface of a gear blank from root to point of a tooth, the portions back of the cutting edge'being suitably relieved, by rotating rotating a member in timed relation in the manner of a grinding member meshing with the gear blank, and in providing feeding motion between said cutting edge and said member in 'the direction of the teeth of the gear blank. In this manner the steps of the grinding process are performed, with the difference of having a formed cutting edge in place of a blank, and of having a test member to be formed in place of the grinding member. 7

Another way of obtaining a thread surface of the described character is by providing a finished gear of the same character as a finsaid cutting edge on the axis-of the blank, by

ished gear blank, by providing flutes in said gear so as to form agreat number of cutting edges covering the whole face of the teeth, by providing relief back of the cutting edges if so desired, and by rotating said gear adj acent a rotating member in the same manner as the gear blank rotates adj acent a rotating -while grinding well at. the. proper high speeds, ceases to grind at veryslow speeds. At very slow speeds the pressure exerted by the truing member on the grinding member loosens the grinding grains in their comparatively soft bed and finally dresses them off or shaves them off, while not being unduly affected by the hardgrains.

this. type is shown A dressing member of at 14 in Fig. 1. It is a hardened and ground gear identical with a finished gear blank, containing in this case unrelieved teeth 25 equal to the teeth 18 of blank 11. y In addition a single helical flute 26 is provided, forming edges 27 on the teeth 25. Dressing member 14-is coaxial with the-blank and secured to the same arbor12. Before or after a blank 4 is finish ground, a very low speed of the grinding member is effected, the blank and dressing member are advanced, so that the dressin member engages the grinding member in t e same manner as the blank engages the grinding member. The latter is then trued or dressed, while a feeding motion is provided.-

Fig.3 illustrates a slightly modified embodiment of my invention. A pair of coaxial grinding members 28, 29 are used, 0 erating on opposite toothsides 30, 31 of di erent teeth 32, 33 of a blank 34, said sides 30, 31 facing towards .each other. With the greater inclination of the grindin profiles, with respect to a plane perpendicu ar to the axis 35 of the grinding members,'increased grinding wheels is thus made, which are noted for their rigidity.

While I have shownconvex tooth profiles 30, 31, concave tooth profiles might also be provided, as indicated in dotted lines 30'.

In the Figures 4 and 5 I have illustrated an applicationof my method to grinding helical gear teeth. The grinding member 36 is then set preferably to the lead'angle in'its center. The numeral'37 denotes a tooth normal, that is perpendicular to the direction of a tooth, in grinding contact. The axis38 of grinding member 36 is inclined at the lead angle 39 to said tooth normal. Grinding member and blank are rotated in timed relation in engagement with one another, and preferably a feeding motion is provided in the direction of the helical teeth of the blank.

Preferably the grinding members are provided with single threads in the applications chiefly considered. Either a single turn or a puralityof turns of a single thread are use One of the difliculties hitherto encountered in grinding gears with a member having grinding portions disposed in a thread, is the fact that a perfectly balanced grinding member gradually gets out of balance afterrepeated truing or dressing. The reason of that,

and the remedy here provided will explained with reference to..the' Figures 6. ,and

7. In the development Fig. 7 the thread .41

of a grinding member is inclined at a small angle to the end periphery 42 of said member. If the thread were continued to the end periphery 42. as indicated in dotted lines 41, then the acute'portion adjacent the-end would-be very weak and might break down at the least knock. For this reason the dotted end of the thread 41 is removed, and the cen-' tral part of the thread, intermediate the top and the bottom, reaches about as far as shaded. The ends of the thread 41 are so shaped as to reach the bottom adually, see Fig. 6, which illustrates a similar grinding member.

When truing in a known manner or also in Q the manner just described, the inclined ends 41" of the thread 41 are-left out in truing, and remain as they are, while stock is removed from all other parts, namely'from the bottom, from the top and from the'sides of the thread. Least grinding material is therefore removed on the side ofthe ends 41" that is to say on the top of the member shown in rigidity of the grindin members ma be ob; tamed. A step in the irection of cylindrical bottoms (see Fig.7) is embodied with grindber. Only a small width 43 of thethread ing stock on the side opposite to ends 41", whereas adjacent these ends the whole'width 4.4-of the thread bottom is embodied by grind- .ing material. In dressing, the additional material to be removed from the thread bottom makes up for the'material lost or left on the ends 41".

Thethread bottoms, it is understood, ordinarily are kept clear of the top or point of the teeth of the blank, and serve only for reinforcing the strength of the rinding thread, and according to the above, Eor keepin the rinding member balanced.

- ifg. 8 1s a'development of the periphery 46 o a truing member of the type shown in Fig. 1. It contains unrelieved straight teeth 47 identical with the teeth of a finished gear blankflcutting edges being formed by asingle helical flute 48, which extends over a plurality of turns.

A truin member of the'same character, I I

posed at different axial positions, and cover' the face of the teeth uniformly. The described restriction is however only then imgortant, when no feed motion is provided in ressing. If feed motion is provided, it is immaterial.

Frequently relief will be provided back of .the cutting edges or dressin edges. When relief is provided, I usua y dispose the edges for dressing one side of a grinding thread on one member, and the edges for dressing the opposite side on another member. The two members are coaxially arranged, and angularly adjustable with respect to one another.

In 10, concentriedisks 54, 55, 56 are provid constituting a truing member for truing one side of a grinding thread. Other disks 58,-

containing relieved edges 57, and A 59, 60 contain relieved edges 61, and constitute a truing member for truing or dreming the opposite side of said thread. Thetwo members are angularl adjustable with re spect to one another a ut'their axis 62, see

sliding motion, which is kept slow. Other the same machine, when providing a, different truing members will now be described with inclination of the axis of the grinding memconjugate to each other, and "do not mesh axis.

Fig. 11. VVhentheedges are unduly scratched ually after completed feed along the teeth through long service,- the faces ofthe disks, of the blankrepresented. are ground off, so that their thickness is v diminished; the disks are again assembled form, and truing is effected through gear and suitably adjusted.

Fig. 12 indicates two sets of disks adapted ing member. for truing a grinding member to grind helical teeth. s cordance with myv invention will now be de- The truing members this far described act scribed with reference to the Figures 15-17 on the grinding members substantially in a Straight tooth gears may also be ground with reference to Figures 13 and 14. These other ber, especially when setting said axis at right truing members act on each other substanangles to the axis of the blank.

tially with rolling contact, and are therefore least apt to get'scratched.

For truing or dresslng, the grinding memnalled in suitable bearings, indicated at 72, ber 64 andt'ruing member 65 are rolled in enand receives power from a motor 73. A

gagement with each other, preferably on change speed gear is provided in a casing 74,

parallel axes 66, 67. The two members 64 for effecting slow truing speed. Member and 65 are fully conjugate to each other, like engages blank secured to an arbor 76, Wh1ch two intermeshing gears turning on parallel is journalled in bearings 77. Preferably a a a d onta t with each other along a positive operative connection is provided beline or lines at a time, which lines gradually tween grinding member 70 and blank 75.

sweep the respective surfaces. The two cy- This connectionconsists in the present inlindrical pitch surfaces 53, 63 roll upon each stance of a worm 78 se ured to shaft 71 0f the other without sliding. The truing action is grmdmg member, of a worm Wheel 79 sehere efi'ectedfthrough pressure, protruding cured to a shaft 80 disposed parallel to the grinding grains being loosened in their bedarbor 76 of the blank, and of a pinion 81 and ding through the pressure exerted by the master gear 82, secured respectively to shaft truing member. 80 and arbor 76. Master gear 82 is preferably The surface of a truing member of the said i f iameter as c m Med wi h the gear type may be determined, by fir t deter i blank 5 and contains helical teeth 83 having ing the grinding surface in the manner dethe same "lead as the teeth 84 of blank 75. scribed, and then from the known grinding The inclination of the teeth 83 of the larger surface det rmining th truing urf as th gear 1s therefore larger than the lnclmatlon of conjugate surface, namely as the tooth 1112 the'teeth 84. In case Of straight teeth of the face'of a gear suited to mesh with the grind blank, the teeth of gear 82 are also straight. ing surface while turning on parallel cen- The bearlngs 77 form part of a sl1de 85, which ter s. I is movable in the direction on theblank arbor The above truing member does not require (76). The latter can therefore be considered feed between truing member d indi movable about its axis and in the direction of member during inning, A t i member f lts axls. Arbor 76 further carr es a member mesh between a truing member and a grind- A grinding member 70 of the character set forth is rotated on an axis 71, which is jour-' A machine for grinding helical gears in 'acthis character may also true or dress the ends 86 rigidly secured to it and containing an ex:

41" (Fig. 6.) of the grinding thread, d ternal thread 87, having a leadequal to, the.

maintains perfect balance of the grinding desired feed P revolution h a k member without special provisions. Thread g g o er Q f L 'Q When feed can be.readilyprovided,then the Wh1ch 1s l y fixedlld mtatable n a truing member may be made conjugate to the 3X15 ,,bY W h Wheel h d teeth of an internal gear, which'is the coun- 88 (11113111137 kelpt a x p l y a terpart of the gear blank If in Fig. 14, the gear center is located at 68, then the'grinding member 64 is conjugate to the external gear having a center 68 and a pitchcircle 69; and the truing member 65 is conjugate to the teeth of an internal gear of the same center 68 and pitch circle 69(- The-diameter of the truing member may be made larger pin 91 disposed on hand wheel 90 and engagmg a suitable hole or recess. A truing.mem-

ber 92 of gear form is secured to arbor 76.

The operation-is as follows: Grinding member 70 is rotated on its axis 71, and through worm 78, worm wheel 79, pinion'81 and master gear 82, the blank 75 is rotated on its'axis in timed relation to the rotation of the grind.- ing member 70. As the blank rotates, the

than the dlameter .5 al gear, as thread 87 advances in the stationary thread 88, shOWn- The two members 65 are not f y and moves arbor 76 in 'thedirection of its On account of the mesh between the with line contact. The respective thread surhelical master gear 82 andpinion 81 feeding faces are not completely covered by rotation motion is thus added to the rotary motions, in a-single relative position, but only gradwhich is a helical motion in the direction of I through the teeth change speed gear is set' for very slow speed,

mem

hand wheel 90 is turned in a direction to move the rinding member adjacent the truing Ear 92, table 93 islifted by a small amount by operating the-two eccentrics 94 on which table 93 rests, and the truing member is slow- 1y passed through the grinding member by further operating hand wheel 90. It is'then returned; the gear blank is taken ofi,'a new blank is put on and placed in starting position. I have shown'the hand wheel 90 directly connected with thread 88 for-simplicitys sake, but usuall. may provide a hand wheel 90 cared to threa 88, and mayfurther make ad- 'tions and refinements, while maintaining the same general principles.

The two eccentrics may be operated with gears in a known manner which needs no explanation, and which does not form part of the principles of my invention. i

A planetary gear for obtaining a suitable slow dressing speed, such as mi ht be laced in casing 74, is diagrammaticailyin icated in Fi 19. For inding, the driving shaft 95 an I driven sha 96 are connected by means of a friction clutch, member 97 having been moved in splines of'planetary cas ng 98 into contact with member 99 keyed to the driven shaft 96. For effecting slow speed, member 97 is moved into contact with stationa stationary, and effecting a large reduction through the enclosed gears 102..

As table 93 is lifted vertically before each truing operation, pinion 81 gradually moves for instance from the position shown in full lines in Fig. 18 to position'81' shown in dotted lines, and thereby rotates the master gear 82 and theblank 75. i Adjustment between grinding member and truing member is then necessary to eliminate the effect of sa d additional rotation, and to dress ofl. equal amountsof.

grinding stock on either side ofthe thread of grinding member 70. Such compensation tionary thread 105. Ordinarily gear 103 i'sv maintained stationary. When it'is rotated. it screwsitself in or out of, thread .105, and

carries pinion 81 along axially.

' pair of hypord miter ,surface 100,- thereby holding planetary casing 98 nection between a grinding member 107and a truing member 108 of the-type indicated in the Figures 13 and 14. Member 108-is conjugate to grinding member 107 and 'suited to mesh with line contact with said member, when both members are rotated on parallel axes-109, 110 in timed relation. Member 107 is shown-in grinding contact with blank 111. Dressing or'truing may be effected during grinding, if so desired. The truing member.

The diagram Figure 21 indicates a gearcon- 108 is geared to grindin member 107 by two bevel gears 112, 113 an two coaxial pinions 114,115 of which pinion 115 is slidable in splines of shaft 116, suitable bearings are provided,'partly shown at 117, 118. .Ordinarily truingmember 108 is in the position indicated in full lines.' For truing it is approached to the grinding member and assumes then a' position as indicated in dotted lines 108'.

A- gear connection: between a grinding member 120 and a dressing member 121 of the type requiring feedin 'motion is indicated in Figure 22. The rive is here effected through two splined shafts 123 123, by means of ahypoid gear124, a hypoid pinion 125, a gears 126, 127, a hypoid pinion 128 and matin gear 129. The pinions 125,128 are slida ly mounted on shafts 122, 123 respectively, being connected to said shafts with splines. The said gear connection permits feeding motion len hwise of shaft 122, and adjustment lengthwlse of shaft 123. Truing is effected by rolling grinding member120'and truing member 121. together, in the direction .of arrows 130, 131.

In Figure '23 means are diagrammatically indicated for effecting reci rocating feed between grinding member an blank, in place of .the continuous feed in onedirection rovided in the embodiment shown in the Figures 15 to 17. The shaft or arbor 76 contains the ar blank and master 'gear 82, and possesses in addition a disk 133 with taperedsides.

Said disk engages a slot 134 of a drum 135 i which is rotate pinion 137 secured to shaft 76, a slidable in splines of shaft 136, and intermediate gears 139. All said gears partake at on its axis 136 by means of a the feed motion of shaft 76. The drum135 1 ordinarily is fixed in axial direction, but may be adjusted axially by hand, with means not indicated. v

As shaft 76 rotates, it also turns shaft 136 by means of the above said gears 137, 138, 139.

Drum 135 is thus rotated in proportion to the rotation of shaft 76, and by movingdifi'erent portions of slot 134 adjacent disk 133,-

the shaft 76 is fed in the direction of its axis. Slot 134 is of the form of a closed groove,

whichfexten'ds on the circumference of the L drum 135.

While I have described my invention particularly as applied to grinding, the same steps may also be employed for lapping gears,

' for burnishing gears, and for cutting gears.

Moreover many further changes and modifications-may be made in my invention by .simply applying the customary practice of the art, and without departing from its spirit. For definition of the scope of my invention it is relied upon the annexed claims.

What I claim is:

1. The method of grinding gears of constant profile, which consists in providing two coaxial members having grinding portions disposed in a thread, in positioning said members so as to engage only opposite sides of different. teeth of a gear blank, the portions simultaneously engaged facing towards each other and beingdisplaced angularly about the axis of said gear blank relatively to each other, in rotating grmdmg members and blank on the respective axes in timed relaftion to each other, and in providing feeding motion between grinding members and blank in the direction of the teeth of theblank.

2. The method of grinding gears, which 5 consists in providing two rotary members having grinding portions disposed in threads, in positioning said members so as to engage only [opposite sides of different teeth of a gear blank, the portions simultaneously engaged facing towards each other'and being displaced angularly about the axis'of said gear blank relatively to each other, and in rotating grinding members and blank on their respective axes in timed relation toeach other.

3. In a. machine for grinding gears, an arbor for holding a gear blank, said arbor being rotatable on its axis and movable in the direction of its axis, a screw thread secured to saidarbor for feeding said arbor in pro- I portion to itsturning motion, and rotatable means engaging said screw thread.

4. In a machine for grinding gears, an arbor for holding a gear blank, said arbor being rotatable on its axis and movable in the direction of its ':lXiS, a master gear of increased diameter as compared with the gear blank, and means for rotating a grinding member and the blank continuously, in timed relation to each other.

5. In a machine for grinding helical gears,

an arbor for holding a gear blank, said arbor being rotatable on its axisand movable in the direction of its axis, a master gear of increased diameter as compared with the gear 65 blank, said master gear having helical teeth of the same lead as the teeth of the blank. and means for continuously rotating the blank and a grinding member, in timed relation to each other.

6. The method of forming gears of constant profile, which consists in providing a rotary member having active, portions disposed in a thread fully conjugate to the tooth surfaces of an accurately finished gear blank in a manner tomesh with'line contact with said tooth surfaces, said thread having a. curved profile in an axial plane, in positioning said member relatively to a gear blank at an angle differing from the angle of its mating gear, by at least thirty degrees (30), in rotating said member in engagement with said gear blank, and in rotating the gear blank on its axis intimed relation to the rotation of said member.

7. The method of forming gears of constant profile, which consists in providing a rotary member having active portions disposed in a thread, the thread profile in an axial plane having a general inclination changing lengthwise of the thread with respect to the axis of said thread, in positioning said member in engagement with a gear blank, in rotating said member, and in rotat ing the gear blank on its axis in timed relation to the rotation of said member.

8. The method of forming gears of constant profile, which consists in providing a rotary member having active portions disposed in a thread protruding over' the tooth surfaces of a rack conjugate toa finished gear blanksaid thread having a concavelycurved profile in an axial plane, in positioning said member in engagement with a gear blank, in rotating said member on an axis angularly disposed to the axis of the gear blank androfiset from said axis, and in rotating the gear blank in timed relation with said member. 1

9. The method of forming gears, which consists in providing a rotary member havaccurately finished gear blank in a manner.

to mesh with line contact with said tooth surfaces, said thread having a curved profile in an axial plane, in positioning said member in engagementwith a gear blank, in rotating-said member, and in rotating the gear blank on its axis in timed relation with said member, the axis. of said gear blank and the axisof said member bearing a dilferent relation to each other than the axis of said gear blank and the axis of its mating gear. 1-1. The method of grinding gears, which consists in providing a rotary member having grinding portions disposed in a thread fully conjugate to the tooth surfaces of an accurately finished gear blank in a manner' to mesh with .line contact-with said tooth surfaces,- the thread profile in anaxial plane being curved and having a general'inclination changing lengthwise of the thread relatively to the axis of said thread, in rotating said member in engagement with a gear blank, in rotating said gear blank on its axis in timed relation to the rotation of said member, and in providing-feeding motion between said gear blank and saidmember along't-he axis of said gear blank.

12. The method of grinding gears of con-- stant profile, which consists in providing a rotary member having grinding portions disposed in a thread fully conjugate to the tooth surfaces of an accuratel finished gear blank in a manner to mesh with line contact with said tooth surfaces, the threadprofile in an axial plane being curved and having a general inclination changin lengthwise of the thread relatively to the axis of said thread, in rotat- -ing said member, in rotating a gear blank on its axis in timed relation to said member, and in feeding the gear blank in. 'a direction lengthwise of its teeth.

to the axis of said thread, in rotating said member in enga ement with a gear'blank, and in rotating gear blank on its axis in timed relation to the rotation of said member.

14. The method of grinding gears, which consists in providing a rotary member having grinding portions disposed inia thread,

the thread profile in an axial plane being curved and having a eneral inclination changing lengthwise of t e thread relatively to the axis of said thread, in rotating, said member, in rotatin a ear blank on its axis in timed relation wit said member, and in providing feeding motion between the blank and rotary mem fully conjugate to the said member alon the teeth of the blank.

The metho of forming gears, which consists in providing a gear blank and a er havin continuous threads final tooth surfaces of said gear blank, said member difierin from the gear intended to run .with the nished gear blank, the thread profile of said member in an axial plane being'curved and having a general inclination changin lengthwisev of the. thread with respect to't e axisof the thread, and in rotating said member in abrasive en agement with said ear blank at the ratio 0 the respective num rs of teeth and threads". I

16. The method of forming gears, which consists in providing -a gear blank and a rotary member having continuous threads fully conjugate to the final tooth surfaces of in an axial plane being curved and having a the direction of the axis of the gear blank.

' v ERNEST VVILDHABER.

said gear blank, said member difierin from the gear intended to run with the "shed gear blank, thethread profile ofsaid member 

